Lithium-ion batteries are used in many commercial applications, such as aerospace, automotive, medical devices, and portable electronics, because of their desirable volumetric and gravimetric energy density performance compared to other rechargeable battery systems. However, further advancements in cell components are needed to address the increasing demands for lithium-ion batteries with higher energy density for several of these technologically important applications. One approach for improving the energy density of lithium-ion batteries involves replacing state-of-the-art electrodes with new electrode materials that offer enhanced energy density performance. Silicon (Si) is one candidate material that is promising as a potential next-generation anode because of its high theoretical capacity (4200 mAh/g) compared to state-of-the-art graphite carbon (327 mAh/g) (see, for example, Poizot et al. 2001, “Searching for New Anode Materials for the Li-Ion Technology: Time to Deviate from the Usual Path,” Journal of Power Sources, 97-98, 235-239 (2001); and Kasavajjula et al. 2007, Nano- and Bulk-Silicon-Based Insertion Anodes for Lithium-Ion Secondary Cells,” Journal of Power Sources, 163(2), 1003-1039 (2007), both incorporated herein by reference). The high specific capacity of Si materials significantly reduces the amount of active anode material required in the electrode, thus increasing the energy density of the battery cell. However, Si anodes have poor cycle life due to large volume changes (>300%) experienced during lithium insertion and extraction, which leads to fracturing and electrical isolation of the active anode particles, thus limiting their use in practical commercial lithium-ion battery applications (see, for example, Huggins 1999, “Lithium Alloy Negative Electrodes,” Journal of Power Sources, 81-82, 13-19 (1999), incorporated herein by reference).
Various approaches described in the literature for improving the cycle life of Si anodes include nanowires grown on conductive substrates, silicon nanoparticles, silicon-carbon (Si—C) composites, and Si in active and inactive matrices (see, for example, U.S. Patent Application Publication No. 2011/0143019 A1, inventors Mosso et al., published Jun. 16, 2011; U. S. Patent Application Publication No. 2012/0183856 A1, inventors Cui et al., published Jul. 19, 2012; U.S. Patent Application Publication No. 2010/0062338 A1, inventors Golightly et al., published Mar. 11, 2010; Wang et al. 1998, “Lithium Insertion in Carbon-Silicon Composite Materials Produced by Mechanical Milling,” Journal of The Electrochemical Society, 145(8), 2751-2758 (1998); U.S. Pat. No. 7,618,678 B2, inventors Mao et al., issued Nov. 17, 2009; U.S. Pat. No. 7,785,661, inventors Carel et al., issued Aug. 31, 2010; Kim et al. 1999, “The Insertion Mechanism of Lithium into Mg2Si Anode Material for Li-Ion Batteries,” Journal of The Electrochemical Society, 146(12), 4401-4405 (1999); Wang et al. 2000, “Innovative Nanosize Lithium Storage Alloys with Silica as Active Centre,” Journal of Power Sources, 88(2), 278-281 (2000); and Chan et al. 2008, “High-Performance Lithium Battery Anodes Using Silicon Nanowires,” Nature Nanotechnology, 3, 31-35 (2008), all incorporated herein by reference). The small nanowires and nanoparticles are designed to reduce stress in the active Si material during extreme volume changes and also allow fast transport of Li-ions during cycling (see, for example, Cui et al. 2008, “Crystalline-Amorphous Core-Shell Silicon Nanowires for High Capacity and High Current Battery Electrodes,” Nano Letters, 9(1), 491-495 (2008), incorporated herein by reference). Si—C composites consist of Si particles embedded in a carbon matrix that maintains electrical contact and provides mechanical support for the active Si particles during cycling.
Other examples of silicon anode preparations include: (1) fabrication of submicron Si pillars on Si wafer substrates using lithography-based methods wherein the formed Si pillars can be used as anode materials while attached on the Si substrate or as free wires after release from the substrate by mechanical methods (sonication or scraping) or chemical etching with hydrofluoric acid, (2) fabrication of Si anodes by coating Si active material onto pre-formed nanostructured, conductive substrates, such as metal silicide nanowires, carbon particles, and carbon nanofibers, (3) formation of porous Si anodes by chemical etching (e.g., acid or plasma gas) of Si powders (see, for example, U.S. Patent Application Publication No. 2009/0068553 A1, inventor Firsich, published Mar. 12, 2009; U.S. Pat. No. 8,101,298 B2, inventors Green et al., issued Jan. 24, 2012; U.S. Patent Application Publication No. 2013/0011736 A1, inventors Loveness et al., published Jan. 10, 2013; and Magasinski et al. 2010, “High-Performance Lithium-Ion Anodes Using a Hierarchical Bottom-Up Approach,” Nature Materials, 9(4), 353-358 (2010), all incorporated herein by reference). The porous Si material may be further processed by coating with a passivating layer, such as carbon or gold (see, for example, U.S. Pat. No. 8,263,265 B2, inventors Mah et al., issued Sep. 11, 2012, incorporated herein by reference). These approaches, however, have yielded limited success in terms of realizing Si anode materials with improved cycle life. Additionally, the described synthesis methods have low production rates, high cost, and in some cases provide poor control over the resulting Si anode structure, which limits their use in practical commercial lithium-ion battery applications (see, for example, Magasinski et al. 2010, “High-Performance Lithium-Ion Anodes Using a Hierarchical Bottom-Up Approach,” Nature Materials, 9(4), 353-358 (2010), incorporated herein by reference). These existing challenges indicate that further improvements are needed to realize Si anode materials with enhanced cycle life.